The first two wave types, P and S, are called body waves because they travel or propagate through the body of Earth. The latter two are called surface waves they the travel along Earth's surface and their amplitude decreases with depth into Earth.
Toysmith Spring Ring Game. Here is a super fun game the kids might like. Nordstrom has this Toysmith Spring Ring Game for $14.98! That is down from the normal price of $24.99, for a 40% savings.
If you like it, you can then opt for something a bit more expensive, like this one from LoveHoney that has several different speeds, a remote control (for you or for her), ribs to add extra intensity and more. Rabbit Rocker Remote Control Vibrating Cock Ring, $38.99 at Lovehoney.com.